This invention relates to an X-ray mask structure, an X-ray exposure method using an X-ray mask structure or an X-ray exposure apparatus, and a device manufacturing method using an X-ray mask structure or an X-ray exposure apparatus.
Due to increasing density and speed of semiconductor integrated circuits, the linewidth of a pattern for integrated circuits is becoming smaller and smaller. Improved performance of semiconductor manufacturing methods is thereby required. In order to meet this need, printing apparatuses, such as steppers using shorter wavelengths, such as KrF lasers (248 nm), ArF lasers (193 nm), and X-ray regions (0.2-15 nm) have been developed.
Also, as regards a resist material to be used for transfer of a desired pattern to a workpiece, a chemical amplification type resist using acid catalyst has been used.
On the other hand, because of decreasing linewidth of a pattern desired, dust protection becomes difficult to accomplish. While the limit for particle size or particle number becomes very strict as a matter of course, also the sensitivity to chemical matters is increasing. Thus, in a clean room for production of semiconductor integrated circuits, chemical contamination is a problem.
The contamination is caused by matters such as those produced by resist decomposition, dispersed matters produced during processes such as development and cleaning, or volatile matters attributable to equipments such as wall material or adhesive agents. If exposure with high-energy X-rays is performed in such an environment for a long period, due to contamination of the surface of a mask, i.e., deposits of materials thereon, the X-ray transmission factor, reflection factor, or scattering will change. Particularly, when a chemical amplification type resist is used, acid is produced, and acid or decomposed material may be evaporated during or after the exposure process, which accelerates contamination of the mask.
FIG. 1 illustrates an example of reaction of a chemical amplification type resist. A material of t-Boc (tetra-butoxy carbonyl styrene) contained in the resist as an anti-solution agent may be decomposed into volatile butene.
Further, since in X-ray projection exposure the exposure process is performed while a mask and a workpiece (wafer) are held with a small gap of about several tens of microns or less, contamination of the mask causes a critical problem. Deposits may have various shapes and compositions. While there may be some dependence upon the environment, details are not clear. It may be considered that the deposits are caused not solely by simple opto-chemical reaction, but by a complicated combination of decomposition, recombination, multiple-order reaction, accumulation and crystallization. Furthermore, since in an X-ray mask the absorptive material used has a high aspect, it is difficult to clean the mask completely. There may remain particles not removed by the cleaning. Also, since the supporting film used is very thin, its strength is very low. Therefore, the cleaning operation can not be performed many times.
Inside the exposure apparatus, contamination of components will cause adverse influence to the performance.
It is an object of the present invention to provide a novel and improved X-ray mask structure or X-ray exposure apparatus by which at least one of the problems described above can be solved or reduced.
It is another object of the present invention to provide an X-ray exposure apparatus using such an X-ray mask structure, or an X-ray exposure method using such an X-ray exposure apparatus.
It is another object of the present invention to provide a device manufacturing method using such an X-ray mask structure or X-ray exposure apparatus.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.